This invention relates to a rotary connector apparatus for supplying electric power to an air bag or the like provided for example in a pad portion of a steering wheel of an automotive vehicle.
Recently, technology to prevent an automotive occupant from suffering collisional impacts by inflating an air bag during an automotive accident has been put to practical use. In the air bag, particularly an air bag provided in a pad portion of a steering wheel, it is necessary to supply electric power to an inflator of the air bag from the vehicular body side of the air bag through a rotary portion of the steering wheel. As a means for supplying electric power, there is one arrangement that principally uses a slip ring and another arrangement that employs a flexible, or soft, cable wound around in a spiral form like the rotary connector apparatus of this invention.
Conventionally, there have been proposed various types of rotary connector apparatuses of this kind. In a rotary connector apparatus disclosed for example by Japanese Utility Model Publication No. H4-54715, there are provided a stator housing, a rotor housing rotatably mounted on the stator housing, and a flexible cable accommodated in a spiral form within a space defined by both of the housings, wherein the rotary connector apparatus is further provided with a guide (peripheral wall) for guiding an end of the flexible cable to the inside of the space as well as an attachment (rotatable ring) for connecting the stator housing and the rotor housing.
The steering portion to which a rotary connector apparatus of this kind is attached is at a point adjacent to a driver's seat, and it is necessary to avoid causing abnormal sound from the rotary connector apparatus. However, in the conventional art stated above, the flexible cable is in direct contact with an inner wall of a housing so that there is a possibility of generating a sliding sound, for example, by the flexible cable. To this end, use of a slidable sheet excellent in slidability, wherein the slidable sheet is adhered to the inner wall of the housing, and a groove is provided at a boundary portion between the slidable sheet and the housing, has been contemplated so as to improve slidability of the flexible cable and thereby prevent generating a sliding sound.
However, where a slidable sheet is adhered to prevent the generation of a sliding sound as in the above conventional art, there are necessarily an adhesive agent and adhesive processes. Further, in order to secure by adhesion over a long term, there has been a concern that appropriate selection of materials for the housing or the adhesive agent is required. Also, there has been a possibility of tangling by a flexible cable falling into the groove at the boundary portion between the slidable sheet and the housing.
Since in the connector apparatus of the kind described above the rotor housing rotates relative to the stator housing, it is in general necessary to form a bearing structure at a contact point between the housings. However, the provision of the bearing increases, for example, the diameter of the axial portion of the rotor housing, which is accompanied by an increase in length of the flexible cable wound around the axial portion. Consequently, the cost required for the flexible cable rises, and the sliding sound generated due to contact by the flexible cable with the housing becomes great.
Each of the rotational connector apparatuses of the kind described above was provided with a cord electrically connecting the rotor housing and the stator housing to external apparatuses, which cord was connected with a holder for holding an end of a flexible cable within the housing, the connection point being covered by a cord cover. However, in the prior art techniques, the holder was mounted on a disk-shaped portion of the housing by securing the cord cover and the holder to each other by means of screws. This increased the size of the rotational connector apparatus in the axial direction.
Each of the rotational connector apparatuses of the kind described above was provided with a holder for holding an end of a flexible cable, and the flexible cable was connected with an external circuit. However, there was a risk that, where the shape of the holder was inappropriate, the holder caught on the flexible cable when the flexible cable was wound or unwound, which damaged the flexible cable. Further, there was also a problem that, when a tongue-shaped elastic piece for preventing buckling of the flexible cable was fixed, if a fixing portion of the tongue-shaped elastic piece protruded from the holder, the fixing portion interfered with the flexible cable.